Fluorescent retroreflective sheet

ABSTRACT

This invention provides encapsulated type fluorescent retroreflective sheeting which is excellent in appearance and weatherability, and which comprises a surface-protective layer disposed on the side on which light is to strike, a binder layer connected to the surface-protective layer through network bonding parts, an air layer which is sealed-up by the network bonding parts between the surface-protective layer and the binder layer, and a retroreflective element layer disposed between the surface-protective layer and the air layer, or between the binder layer and the air layer, wherein at least one layer located on the light-incident side of sealed-up air layer contains at least one fluorescent dye selected from the group consisting of benzimidazole coumarin type-fluorescent dyes of formula (1) as follows:  
                 
 
     and benzopyran type-fluorescent dyes of formula (2) as follows:

TECHNICAL FIELD

[0001] The present invention relates to novel fluorescentretroreflective sheeting. In more detail, this invention relates tonovel fluorescent retroreflective sheeting which contains a fluorescentdye of specific structure.

[0002] In particular, this invention relates to novel fluorescentretroreflective sheeting which is constituted of cube-cornerretroreflective elements or micro glass beads retroreflective elements,and which is useful for signs including traffic signs and constructionwork signs, license plates of automobiles and motorcycles, safetymaterials of clothing and life preservers, markings of signboards, andreflectors for visible-light-, laser-beam- or infrared-ray-reflectivesensors.

BACKGROUND ART

[0003] Retroreflective sheeting for reflecting incoming light towardlight source has been well known, and such sheeting with use of itsretroreflective characteristics has been widely applied in theabove-mentioned fields.

[0004] Generally, basic optical properties which are required ofretroreflective sheeting include both high brightness in night time,i.e., the intensity of reflective brightness represented by reflectivebrightness against light which is being frontally incoming toward saidsheeting, and wide angularity. With regard to wide angularity, there aredemanded three properties, i.e., observation angularity, entranceangularity and rotational angularity. Good visibility of sheeting in daytime is also required.

[0005] There have been reported some methods to improve the visibilityof retroreflective sheeting in day time. A known one among them is togive fluorescent appearance by means of including fluorescent dye insome layer or other of retroreflective sheeting.

[0006] U.S. Pat. No. 3,830,682 of Rowland, for instance, discloses thatfluorescent retroreflective sheeting of clear color tone is produced bycompounding fluorescent dye such as Rhodamine B Extra, Rhodamine 6DGN,Fluorol 7GN and Amaplast Orange LFP in prism layer oftriangular-pyramidal cube-corner retroreflective sheeting.

[0007] U.S. Pat. No. 5,387,458 of Pavalka discloses fluorescentretroreflective sheeting of clear color tone which is constituted of ascreen layer which absorbs ultraviolet ray although substantiallytransparent to visible light, and of triangular-pyramidal cube-cornerretroreflective sheeting elements layer to which thioindigoid type-,thioxanthene type-, benzoxazole coumarin type- or perylene imidetype-dye has been added.

[0008] U.S. Pat. No. 5,605,761 of Burns discloses fluorescentretroreflective sheeting of clear color tone wherein thioxanthone type-,perylene imide type- or thioindigoid type-fluorescent dye and hinderedamine type light stabilizer have been added to triangular-pyramidalcube-corner retroreflective elements layer.

[0009] U.S. Pat. No. 5,672,643 of Burns discloses fluorescentretroreflective sheeting of color tone in a specific range whereinretroreflective elements layer of cube-corner retroreflective sheetingcontains a combination of perylene imide type-fluorescent dye of aspecific structure with a specific fluorescent dye which is selectedfrom Lumogen F Yellow 083, CI Solvent Yellow 160:1, CI Solvent Green 4,CI Pigment Yellow 101, CI Solvent Yellow 131, CI Solvent Yellow 98,Oraset Yellow 8GF, CI Solvent Green 5 and Golden Yellow D304.

[0010] None of the fluorescent retroreflective sheeting which has beenproposed in the above-mentioned patents simultaneously satisfies bothrequirements of excellent fluorescent appearance and weatherability tomaintain fluorescent color.

[0011] Inventors of the present invention have made assiduous studyabout fluorescent dye which is usable for retroreflective sheeting, andwhich has both properties of excellent fluorescent appearance andweatherability to maintain fluorescent color for a long period of time.As a result, they have found out that a certain kind of benzimidazolecoumarin type- and benzopyran type-fluorescent dyes have both of theabove-mentioned properties, and have thus completed this invention.

DISCLOSURE OF INVENTION

[0012] This invention provides encapsulated type fluorescentretroreflective sheeting which comprises a surface-protective layerdisposed on the side on which light is to strike, a binder layerconnected to the surface-protective layer through network bonding parts,an air layer which is sealed-up by the network bonding parts between thesurface-protective layer and the binder layer, and a retroreflectiveelement layer disposed between the surface-protective layer and the airlayer, or between the binder layer and the air layer, wherein at leastone layer located on the light-incident side of sealed-up air layercontains at least one fluorescent dye selected from the group consistingof benzimidazole coumarin type-fluorescent dyes of formula (1) asfollows:

[0013] wherein R¹ and R² each denote hydrogen atom, alkyl group, allylgroup, cycloalkyl group, cyclohexylphenyl group or alkylphenyl group;and R³ and R⁴ each denote hydrogen atom, halogen atom, alkyl group oralkoxy group,

[0014] and benzopyran type-fluorescent dyes of formula (2) as follows:

[0015] wherein Y¹ and Y²each denote hydrogen atom, cyano group, alkylgroup, alkoxy group, allyl group, allyloxy group, carboalkoxy group,acetoxy-substituted alkyl group, cycloalkyl group or phenyl group; andY³ and Y⁴ each denote hydrogen atom, halogen atom, alkoxy group, cyanogroup or nitro group.

BRIEF EXPLANATION OF DRAWINGS

[0016]FIG. 1 is a cross section of fluorescent retroreflective sheetingof this invention whose retroreflective element layer is constituted ofcube-corner type retroreflective elements.

[0017]FIG. 2 is a cross section of fluorescent retroreflective sheetingof this invention whose retroreflective element layer is constituted ofmicro glass beads type retroreflective elements.

[0018]FIG. 3 is a chart which shows the result of measurement ofreflection spectrum of fluorescent retroreflective sheeting of Example 1and Comparative Example 1.

DETAILED DESCRIPTION OF INVENTION

[0019] In the following, the fluorescent retroreflective sheeting ofthis invention is explained in more detail.

[0020] This invention gives fluorescent color to encapsulated typefluorescent retroreflective sheeting which comprises asurface-protective layer disposed on the side on which light is tostrike, a binder layer connected to the surface-protective layer throughnetwork bonding parts, an air layer which is sealed-up by the networkbonding parts between the surface-protective layer and the binder layer,and a retroreflective element layer disposed between thesurface-protective layer and the air layer, or between the binder layerand the air layer, by means of including benzimidazole coumarintype-fluorescent dye of formula (1) and/or benzopyran type-fluorescentdye of formula (2) in a layer located on the light-incident side ofsealed-up air layer.

[0021] There is no special restriction on the constitution ofencapsulated type fluorescent retroreflective sheeting to whichfluorescent color is to be given in accordance with this invention, solong as said sheeting is basically constituted in the above-mentionedmanner. This invention is applicable to any known retroreflectivesheeting.

[0022] Benzimidazole coumarin type-fluorescent dye of formula (1) withwhich to give fluorescent color to retroreflective sheeting may be anyknown one [see Japanese Patent Application Publication No. Sho 42(1967)-23606 (=U.S. Pat. No. 3,458,880; DE-B-1,469,770)]. Examples ofthis dye are shown as follows: TABLE 1 (1)

Compound No. R¹ R² R³ R⁴ 1-1 C₄H₉ C₄H₉ H CH₃ 1-2 C₂H₅ C₂H₅ H SO₂CH₃ 1-3C₂H₅ C₂H₅ H H 1-4

CH₃ H H 1-5 C₂H₅ C₂H₅ H Br

[0023] Among the above, a yellow fluorescent dye of formula (1) whereinR¹ and R² each denote ethyl group and R³ and R⁴ each denote hydrogenatom is in particular suitable for this invention. This dye is on themarket under a tradename of “Kayaset SF-G” (manufactured by Nihon KayakuK.K.), “Sumikaron Brilliant Flavine 8GFF” (manufactured by SumitomoKagaku Kogyo K.K.), etc.

[0024] Benzopyran type-fluorescent dye of formula (2) with which to givefluorescent to retroreflective sheeting may also be any known one [seeJapanese Patent Application Publication No. Sho 62 (1987)-12822,Japanese Patent Application Publication No. Sho 61 (1986)-58099,Japanese Patent Application Laid-Open (Kokai) No. Sho 57 (1982)-31958].Examples of this dye are shown as follows: TABLE 2 (2)

Compound No. Y¹ Y² Y³ Y⁴ 2-5 H₂═CH—CH₂ H₂C═CH—CH₂ H —OCH₃ 2-1 H₂═CH—CH₂H₂C═CH—CH₂ H H 2-2 C₂H₅ C₂H₅ Cl Cl 2-3 C₂H₄OCH₃ C₂H₄OCH₃ Cl Cl 2-4H₂C═CH—CH₂ H₂C═CH—CH₂ Cl Cl

[0025] Among the above, a red fluorescent dye of formula (2) wherein Y¹and Y² each denote allyl group and Y³ and Y⁴ each denote hydrogen atomis in particular suitable for this invention. This dye is on the marketunder a tradename of “Kayaset SF-B” (manufactured by Nihon Kayaku K.K.).

[0026] The amount of the above-mentioned fluorescent dye of formula (1)or (2) is not strictly limited, but may be varied in a broad rangeaccording to the use of the retroreflective sheeting of this inventionor according to the desired degree of fluorescence. Usually, however, itis preferably within a range of 0.01 to 0.5 PHR, in particular 0.02 to0.4 PHR.

[0027] In the encapsulated type retroreflective sheeting of thisinvention, benzimidazole coumarin type-fluorescent dye of formula (1)and benzopyran type-fluorescent dye of formula (2) may each be usedeither singly or in combination of two kinds or more, or, furthermore,in combination with other fluorescent dye or non-fluorescent dye or withpigment.

[0028] Retroreflective layer and/or surface-protective layer and/orfluorescent dye-containing layer of the retroreflective sheeting of thisinvention may, if necessary, include ultraviolet absorber for thepurpose of improving weatherability etc. Examples of ultravioletabsorber which may be contained are as follows:

[0029] Hydroquinone Type:

[0030] Hydroquinone, hydroquinone disalicylate, etc.

[0031] Salicylic Acid Type:

[0032] Phenyl salicylate, paraoctylphenyl salicylate, etc.

[0033] Benzophenone Type:

[0034] 2-Hydroxy-4-methoxybenzophenone;

[0035] 2-hydroxy-4-n-octoxybenzophenone;

[0036] 2-hydroxy-4-methoxy-2′-carboxybenzophenone;

[0037] 2,4-dihydroxybenzophenone;

[0038] 2,2′-dihydroxy-4,4′-dimethoxybenzophenone;

[0039] 2-hydroxy-4-benzoyloxybenzophenone;

[0040] 2,2′-dihydroxy-4-methoxybenzophenone;

[0041] 2-hydroxy-4-methoxy-5-sulfonbenzophenone;

[0042] 2,2′,4,4′-tetrahydroxy-benzophenone;

[0043] 2,2′-dihydroxy-4,4′-dimethoxy-5-sodium sulfobenzophenone;

[0044] 4-dodecyloxy-2-hydroxybenzophenone;

[0045] 2-hydroxy-5-chlorobenzophenone; etc.

[0046] Benzotriazole Type:

[0047] 2-(2′-Hydroxy-5′-methylphenyl)benzotriazole;

[0048] 2-(2′-hydroxy-5′-methylphenyl)-5-butylcarboxylate benzotriazole;

[0049] 2-(2′-hydroxy-5′-methylphenyl)-5,6-dichlorobenzotiazole;

[0050] 2-(2′-hydroxy-5′-methylphenyl)-5-ethylsulfonbenzotriazole;

[0051] 2-(2′-hydroxy-5′-tert-butylphenyl)-5-chlorobenzotrizole;

[0052] 2-(2′-hydroxy-5′-tert-butylphenyl)benzotriazole;

[0053] 2-(2′-hydroxy-5′-amylphenyl)benzotriazole;

[0054] 2-(2′-hydroxy-3′,5′-dimethylphenyl)-5-methoxybenzotriazole;

[0055] 2-(2′-methyl-4′-hydroxyphenyl)benzotriazole;

[0056] 2-(2′-stearyloxy-3′,5′-dimethylphenyl)-5-methylbenzotriazole;

[0057] 2-(2′-hydroxy-5-phenylcarboxylate)benzotriazole ethylester;

[0058] 2-(2′-hydroxy-3′-methyl-5′-tert-butylphenyl)benzotriazole;

[0059] 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole;

[0060] 2-(2′-hydroxy-5-methoxyphenyl)benzotriazole;

[0061] 2-(2-hydroxy-5′-phenylphenyl)-5-chlorobenzotriazole;

[0062] 2-(2′-hydroxy-5′-cyclohexylphenyl)benzotriazole;

[0063] 2-(2′-hydroxy-4′,5′-dimethylphenyl)5-butylbenzotriazolecarboxylate;

[0064] 2-(2′-hydroxy-3′,5′-dichlorophenyl)benzotriazole;

[0065] 2-(2′-hydroxy-4′,5′-dichloro)benzotriazole;

[0066] 2-(2′-hydroxy-3′,5′-dimethylphenyl)-5-ethylsulfon benzotriazole;

[0067] 2-(2′-hydroxy-5′-phenylphenyl)benzotriazole;

[0068] 2-(2′-hydroxy-4′-octoxyphenyl)benzotriazole;

[0069] 2-(2′-hydroxy-5′-methoxyphenyl)-5-methylbenzotriazole,

[0070] 2-(2′-hydroxy-5′-methylphenyl)-5-benzotriazole carboxylate,

[0071] 2-(2′-acetoxy-5′-methylphenyl)benzotriazole;

[0072] 2-(2′-hydroxy-3′,5′-di-tertbutylphenyl)-5-chlorobenzotriazole;etc.

[0073] Cyano Acrylate Type:

[0074] 2-Cyano-3,3-diphenylethylacrylate;

[0075] 2-cyano-3,3-diphenylacrylate 2-ethylhexyl; etc.

[0076] Among the above-recited ultraviolet absorbers, those ofbenzophenone type and of benzotriazole type are suitable. In particular,2,3′-dihydroxy-4,4′-dimethoxybenzophenone;2,2′-dihydroxy-4-methoxybenzophenone; and2,2′,4,4′-tetrahydroxy-benzophenone are effective among benzophenonetype. In benzotriazole type,2-(2′-hydroxy-5′-methylphenyl)benzotriazole;2-(2′-hydroxy-5-methylphenyl)-5,6dichlorobenzotriazole;2-(2-hydroxy-5′-tert-butylphenyl)benzotriazole;2-(2′-hydroxy-3′-methyl-5′-tert-butylphenyl)benzotriazole;2-(2′-hydroxy-3′,5′-di-tertbutylphenyl)-5-chlorobenzotriazole;2-(2′-hydroxy-5′-phenylphenyl)-5-chlorobenzotriazole;2-(2′-hydroxy-5′-octoxyphenyl)benzotriazole; etc are effective.

[0077] As ultraviolet absorbers on the market, those of benzotriazoletype or of benzophenone type are usable. Examples of ultravioletabsorbers of benzotriazole type include Sea Sorb 701, 702, 708, 704, 706and 709 manufactured by Cypro Kasei K.K.; Adeka Stab LA31 and LA32manufactured by Asahi Denka Kogyo K.K.; Sumi Sorb 250 manufactured bySumitomo Kagaku K.K.; and Bio Sorb 590 manufactured by Kyodo YakuhinK.K.; etc. Examples of benzophenone type include Adeka Stab 1413 andLA51 manufactured by Asahi Denka K.K.; Sea Sorb 101 and 103 manufacturedby Cypro Kasei K.K.; and Sumi Sorb 110S manufactured by Sumitomo KagakuK.K.; etc.

[0078] These ultraviolet absorbers are preferably added in an amount ofusually 0.01 to 2 PHR, especially 0.01 to 1 PHR, more desirably 0.01 to0.95 PHR.

[0079] If necessary, for the purpose of improving weatherability etc., ahindered amine light stabilizer may be included in a fluorescentdye-containing layer of the retroreflective sheeting of this invention.For such use, a piperidine type hindered amine light stabilizer oftertiary amine structure which has a molecular weight of at least 600 isin particular preferable since it keeps weatherability. As examples ofusable hindered amine light stabilizer, those having the followingstructural formulae can be mentioned.

[0080] Examples of hindered amine light stabilizer on the market includeCinubin 622LD, 765, 144, Kimasorb 119FL manufactured by Nihon Ciba GeigyK.K.; Adeka Stab LA52 and LA62 manufactured by Asahi Denka Kogyo K.K.;and Sanol LS2626 manufactured by Sankyo K.K.

[0081] These hindered amine light stabilizers may be included in afluorescent dye-containing layer, usually in an amount of 0 to 1 PHR,preferably 0.1 to 1 PHR, especially desirably 0.2 to 0.8 PHR, eithersingly or in combination with ultraviolet absorber or antioxidant.

[0082] The above-mentioned light stabilizers can be introduced, in theform of ester with (meth)acrylic acid, into skeleton of resin whichconstitutes a fluorescent dye-containing layer As examples of suchreactive type light stabilizers, there can be mentioned1,2,2,6,6-pentamethylpiperidyl methacrylate and2,2,6,6-tetramethylpiperidyl methacrylate. When copolymerized with otherresin-constituent reactive monomers such as (meth)acrylates, vinylacetate and vinyl chloride, these light stabilizers is capable ofintroducing a group of light stabilizer into resin skeleton.

[0083] With a view to giving weatherability, benzoate type lightstabilizer may be compounded in a fluorescent dye-containing layer.Examples of usable benzoate type light stabilizer include benzoate typequencher such as Cinubin 120 (trademark) manufactured by Nihon CibaGeigy K.K.

[0084] In the following, the fluorescent retroreflective sheeting ofthis invention is explained in more detail, with reference to drawingsif necessary.

[0085] First, the retroreflective sheeting of this invention isexplained with respect to an embodiment of suitable structure ofcube-corner type retroreflective sheeting, with reference to FIG. 1which is a cross section thereof.

[0086] In FIG. 1, (3) shows retroreflective element layer in whichtriangular-pyramidal cube-corner type retroreflective elements arearranged in a closest-packing manner. Depending on the purpose of use ofretroreflective sheeting and on circumstances under which to useretroreflective sheeting, there may be provided, on this retroreflectiveelement layer (3), a surface-protective layer (1), a printed layer (2)for the purpose of conveying information to observer or of sheetcoloring, a binder layer (6) for forming a sealing structure to preventmoisture from penetrating the back side of retroreflective element layer(3), a supporter layer (7) to support the binder layer (6), and anadhesive layer (8) and a releasing liner (9) by which to stick saidretroreflective sheeting on another construct (For further details, seeWO98/18028 for instance).

[0087] Printed layer (2) is usually disposed either betweensurface-protective layer (1) and retroreflective element layer (3), oron surface-protective layer (1) or on the reflection side ofretroreflective element layer (3), by means of gravure printing, screenprinting or ink jet printing.

[0088] Cube-corner type retroreflective elements layer (3) may beconstituted of polycarbonate resin, acrylic resin, vinyl chloride resinor urethane resin. This retroreflective elements layer (3) may contain,with a view to improving weatherability, an additive such as anultraviolet absorber, a light stabilizer and an oxidation inhibitor,each added either singly or in combination. There may also be contained,as a coloring agent, various kinds of organic pigments, inorganicpigments, fluorescent pigments, non-fluorescent dyes, and fluorescentdyes other than those of the above-mentioned formulae (1) and (2).

[0089] Surface-protective layer (1) may be made of the same resin asused for retroreflective elements layer (3), and may contain, with aview to improving weatherability, an additive such as an ultravioletabsorber, a light stabilizer and an oxidation inhibitor, each addedeither singly or in combination. There may also be contained, as acoloring agent, various kinds of organic pigments, inorganic pigments,fluorescent pigments, non-fluorescent dyes, and fluorescent dyes otherthan those of the above-mentioned formulae (1) and (2).Surface-protective layer (1) may be divided into two or more layers, inwhich case each of the layers may contain the above-mentioned variouskinds of additives and coloring agents either singly or in combination.

[0090] The material with which to constitute retroreflective elementslayer (3) is not restricted in particular, so long as it satisfiesflexibility which is one of objectives of this invention. Generally,however, said material preferably has optical transparency anduniformity. Examples of material to constitute retroreflective elementslayer (3) include polycarbonate resin, vinyl chloride resin,(meth)acrylic resin, epoxy resin, styrene resin, polyester resin,fluoroplastic, olefin resin such as polyethylene resin and polypropyleneresin, cellulose resin and urethane resin, among which polycarbonateresin, (meth)acrylic resin, vinyl chloride resin and urethane resin arepreferable.

[0091] In order to satisfy the condition of total internal reflection, aretroreflective elements layer (3) has generally an air layer (5)disposed on the back side of cube-corner type retroreflective elements.With a view to preventing the occurrence of inconveniences such asdecrease in critical angle and the corrosion of metal layer which arecaused by moisture penetration under use conditions, a retroreflectiveelements layer (3) and a binder layer (6) are preferably sealed withnetwork bonding parts (4)

[0092] As methods for this sealing, there may be employed those whichare disclosed in U.S. Pat. Nos. 3,190,178, 4,025,159, and in JapaneseUtility Model Application Laid-Open No. Sho 50 (1975)-28669, etc.Examples of resins which are used for the preparation of a binder layer(6) include (meth)acrylic acid, polyester resin, alkyd resin and epoxyresin. Bonding parts (4) may be formed by embossing. Retroreflectiveelements layer (3) and a binder layer (6) may be sealed by any knownmethod, which is to be selected appropriately from heat-fusible resinsealing method, thermosetting resin sealing method, ultraviolet-curingresin sealing method and electron rays-curing resin sealing method.

[0093] Binder layer (6) which is used for this invention may be formedeither over the whole surface of supporter layer (7) or selectively onthe parts of connection with retroreflective elements layer (3), i.e.,on the bonding parts (4), by means of a method such as printing.

[0094] Examples of material to constitute supporter layer (7) includefilm which is made of the same resin as constitutes retroreflectiveelements layer (3) or which comprises general film-formable resin, orplate, fiber, cloth, foil or plate of metal such as stainless steel andaluminum, which are to be used either singly or as a complex.

[0095] As an adhesive layer (8) and a releasing liner (9) by which tostick the retroreflective sheeting of this invention on metal plate,wood plate, glass plate or plastic plate, any known one may be selectedappropriately. An adhesive for adhesive layer (8) may be chosen frompressure-sensitive adhesive, heat-sensitive adhesive and cross-linkingtype adhesive. Examples of pressure-sensitive adhesive include apolyacrylic acid ester self-adhesive which is prepared by thecopolymerization of acrylic acid ester such as butyl acrylate,2-ethylhexyl acrylate, isooctyl acrylate and nonyl acrylate, withacrylic acid or vinyl acetate; a silicone resin self-adhesive; andrubber type self-adhesive. As heat-sensitive adhesive, there may be usedone which comprises acrylic-, polyester type- or epoxy type-resin.

[0096] According to this invention, in a cube-corner typeretroreflective sheeting which has the above-mentioned constitution, atleast one fluorescent dye which is selected from benzimidazole coumarintype-fluorescent dye of the foregoing formula (1) and benzopyrantype-fluorescent dye of formula (2) is compounded in the afore-mentionedmanner, together with ultraviolet absorber and/or light stabilizer ifnecessary, in a layer located on the light-incident side (which isindicated by arrow mark 10 in FIG. 1) of sealed-up air layer (5), i.e.,in at least one layer of surface-protective layer (1), printed layer (2)and retroreflective element layer (3), preferably retroreflectiveelement layer (3), and, thus, there is obtained a cube-corner typefluorescent retroreflective sheeting which is excellent both influorescent appearance and in weatherability of fluorescent color.

[0097] The above-mentioned fluorescent dyes may be kneaded with resinand melted, or may be dispersed in a resin mix liquid and thendissolved, or may be first dissolved with a solvent and then mixed in aresin mix liquid, and are thus compounded in the above-mentioned layer,e.g., retroreflective element layer.

[0098] The fluorescent dyes may be dispersed uniformly on a layer suchas retroreflective element layer. Otherwise, a said fluorescentdye-containing fluorescent-colored resin film which has been preparedseparately may be superposed on surface-protective layer or onretroreflective element layer. Furthermore, one side ofsurface-protective layer or of retroreflective element layer may becoated with a said fluorescent dye-containing resin solution which hasbeen prepared separately.

[0099] Next, an embodiment of another suitable structure of micro glassheads type retroreflective sheeting is explained with reference to FIG.2 which is a cross section thereof.

[0100] In FIG. 2, (3) shows retroreflective element layer on which microglass beads type retroreflective elements, a part of whose glass beadshas been mirror-finished, are arranged in a closest-packing manner.Depending on the purpose of use of retroreflective sheeting and oncircumstances under which to use retroreflective sheeting, there may beprovided, on this retroreflective element layer (3), asurface-protective layer (1), a printed layer (2) for the purpose ofconveying information to observer or of sheet coloring, a binder layer(6) for forming a sealing structure to prevent moisture from penetratingthe back side of retroreflective element layer (3), a supporter layer(7) to support the binder layer (6), and an adhesive layer (8) and areleasing liner (9) by which to stick said retroreflective sheeting onanother construct. [For further details, see Japanese Patent ApplicationLaid-Open No. Hei 8 (1996)-86910 (=U.S. Pat. No. 5,824,390; EP-A-693697)].

[0101] Each layer which constitutes this micro glass beads typeretroreflective sheeting may be made of the same material as mentionedabove with regard to corresponding layers of cube-corner typeretroreflective sheeting.

[0102] According to this invention, in a micro glass beads typeretroreflective sheeting which is shown by this FIG. 2, at least onefluorescent dye which is selected from benzimidazole coumarintype-fluorescent dye of the foregoing formula (1) and benzopyrantype-fluorescent dye of formula (2) is compounded in the above-mentionedmanner, together with ultraviolet absorber and/or light stabilizer ifnecessary, in at least one layer located on the light-incident side(which is indicated by arrow mark 10 in FIG. 2) of sealed-up air layer(5), i.e., in surface-protective layer (1) and/or printed layer (2), inthe same manner as in cube-corner type retroreflective sheeting, and,thus, there is obtained a micro glass beads type fluorescentretroreflective sheeting which is excellent both in fluorescentappearance and in weatherability of fluorescent color.

[0103] In the following, this invention is explained in more detail bymeans of working examples.

EXAMPLE 1

[0104] With use of Henschel mixer, a high-speed rotation type mixermanufactured by Mitsui Kozan K.K., there were mixed 100 parts by weightof “Upiron H3000”, a bisphenol type polycarbonate resin manufactured byMitsubishi Engineering Plastic K.K., 0.1 part by weight of “KayasetSF-B”, a benzopyran type red fluorescent dye manufactured by NihonKayaku K.K., 0.1 part by weight of “Kayaset SF-G”, a benzimidazolecoumarine type yellow fluorescent dye manufactured by the same, and 0.5part by weight of “SanolLS2626”, a tetramethyl piperidine type hinderedamine manufactured by Sankyo K.K., under a condition of 100 rpm for 15minutes.

[0105] Thus produced resin mixture was extruded from nozzle having abore of 4 mm under a condition of extrusion temperature of 240° C. androtation of 35 rpm, with use of a monoaxial extruder provided with ascrew having a ratio of screw length to bore of 30:1 and a compressionrate of 3.0. Thus extruded resin mixture was water-cooled and cut, and,in this manner, there were obtained colored pellets.

[0106] These colored pellets were dried under a condition of 80° C. for12 hours, and were then extruded under a condition of extrusiontemperature of 240° C. and rotation of 50 rpm, with use of a monoaxialextruder provided with a screw having a ratio of screw length to bore of30:1 and a compression rate of 3.0, and, thus, there was obtainedpolycarbonate resin sheeting having a thickness of 200 μm.

[0107] On the surface layer of this colored polycarbonate resin film,there was superposed an 50 μm-thick acrylic resin film (“Sundulen 007”manufactured by Kanegafuichi Kagaku Kogyo K.K.) by heat adhesion methodwith use of a pair of heat rolls set at 200° C. Thereafter, theresultant sheeting was subjected to compression molding with use of amold which was provided, on its surface, with triangular-pyramidal typeretroreflective elements, under a condition of molding temperature of200° C. and molding pressure of 50 kg/cm², in such a manner thatpolycarbonate resin was kept in contact with mold surface. Aftertemperature was lowered to 30° C. under pressure, resin sheeting wastaken out, and, thus, there was obtained polycarbonate resin-madefluorescent triangular-pyramidal type cube-corner retroreflectivesheeting which was provided, on its surface, with a large number oftriangular-pyramidal type retroreflective elements in a closest-packingmanner.

[0108] Separately, “Byron GA2310”, a polyester resin type hot-meltadhesive manufactured by Toyo Boseki K.K., was applied and superposed byextrusion method, in a thickness of 35 μm, on 38 μm-thick whitepolyethylene terephthalate film manufactured by Diafoil Hoechst Co.,and, thus, there was formed a binder-laminated supporter layer film.

[0109] The above-mentioned triangular-pyramidal type cube-cornerretroreflective sheeting and binder-laminated supporter layer film werepassed through a molding roll provided with net-work protrusions and asilicone roll, and, thus, there was obtained encapsulated typefluorescent cube-corner type retroreflective sheeting.

COMPARATIVE EXAMPLE 1

[0110] “Diamond Grade #3924” (fluorescent orange color), a fluorescentcube-corner type retroreflective sheeting on the market manufactured bySumitomo 3M K.K., was prepared as a comparative example.

[0111] The above-mentioned fluorescent cube-corner type retroreflectivesheeting was measured for color clarity and weatherability by thefollowing method.

[0112] [Method for Measurement of Reflection Spectrum]

[0113] With use of a double-beam type spectrophotometer CMS-35MXIIprovided with concave diffraction grating manufactured by MurakamiShikisai Gijutsu Kenkyujo K.K., there was determined reflection spectrumin a wave-length range for measurement of 390 to 730 nm and at awave-length interval of 10 nm, by use of xenon lamp containingultraviolet ray, under light source condition of incident angle of 45°and light receiving angle of 0°. There was also found a wave length (λmax) which showed maximum reflection rate.

[0114] [Color Measurement]

[0115] From the above-mentioned reflection spectrum, there were foundtristimulus values (X, Y, Z) and chromaticity coordinates (x, y, z) bymeans of color measurement based on spectrocolorimetry specified in JISZ8722-1994 of the Japanese Industrial Standards. For this measurement,there was employed a condition of standard light D65 and viewing filedof 2°.

[0116] [Weatherability Evaluation]

[0117] Samples to be evaluated were subjected to 3,000-hour exposuretreatment with use of Atlas Weatherometer of Ci65A type manufactured byToyo Seiki K.K., provided with 6.5 kW xenon lamp. Color measurementbefore and after test was conducted by visual observation, and, thus,the samples were graded as follows. AAA: Only a little change was seenin color and fluorescent sense. AA: Color change was little whilefluorescent sense disappeared. A: Fluorescent sense remained while colortone changed. B: Both color and fluorescent sense changed. C: Colorfaded and whitened.

[0118] Table 3 shows color measurement values and evaluation ofweatherability of fluorescent cube-corner type retroreflective sheetingof the above-mentioned Example 1 and Comparative Example 1. FIG. 3 showsmeasurement results of reflection spectrum. In Example 1, maximumreflection wave-length was 620 nm, and maximum reflection rate was 165%.In Comparative Example 1, maximum reflection wave-length was 610 nm, andmaximum reflection rate was 104%. TABLE 3 Example 1 Comparative Example1 λ max (nm) 620 610 Maximum reflection rate (%) 165 104 X 69.48 48.58 Y39.83 29.30 Z 1.49 0.91 x 0.627 0.617 y 0.359 0.372 z 0.013 0.012Evaluation of weatherability AA A

[0119] As mentioned above, the reflection spectrum of fluorescentcube-corner type retroreflective sheeting of this invention showed muchhigher maximum reflection rate than the retroreflective sheeting ofComparative Example 1. Y value, which indicates the lightness (clarity)of sheeting, of the sheeting of this invention was 39.83, which was muchlarger than 29.30 of Comparative Example 1. The sheeting of thisinvention was excellent also in color change after weatherability test.

1. Encapsulated type fluorescent retroreflective sheeting whichcomprises a surface-protective layer disposed on the side on which lightis to strike, a binder layer connected to the surface-protective layerthrough network bonding parts, an air layer which is sealed-up by thenetwork bonding parts between the surface-protective layer and thebinder layer, and a retroreflective element layer disposed between thesurface-protective layer and the air layer, or between the binder layerand the air layer, wherein at least one layer located on thelight-incident side of sealed-up air layer contains at least onefluorescent dye selected from the group consisting of benzimidazolecoumarin type-fluorescent dyes of formula (1) as follows:

wherein R¹ and R² each denote hydrogen atom, alkyl group, allyl group,cycloalkyl group, cyclohexylphenyl group or alkylphenyl group; and R³and R⁴ each denote hydrogen atom, halogen atom, alkyl group or alkoxygroup, and benzopyran type-fluorescent dyes of formula (2) as follows:

wherein Y¹ and Y² each denote hydrogen atom, cyano group, alkyl group,alkoxy group, allyl group, allyloxy group, carboalkoxy group,acetoxy-substituted alkyl group, cycloalkyl group or phenyl group; andY³ and Y⁴ each denote hydrogen atom, halogen atom, alkoxy group, cyanogroup or nitro group.
 2. Fluorescent retroreflective sheeting of claim 1wherein the benzimidazole coumarin type-fluorescent dye of formula (1)is a yellow fluorescent dye of formula (1) wherein R¹ and R² each denoteethyl group and R³ and R⁴ each denote hydrogen atom.
 3. Fluorescentretroreflective sheeting of claim 1 wherein the benzopyrantype-fluorescent dye of formula (2) is a red fluorescent dye of formula(2) wherein Y¹ and Y² each denote allyl group and Y³ and Y⁴ each denotehydrogen atom.
 4. Fluorescent retroreflective sheeting of claim 1wherein at least one layer located on the light-incident side ofsealed-up air layer contains said fluorescent dye in an amount of 0.01to 0.5 PHR.
 5. Fluorescent retroreflective sheeting of claim 1 whereinfluorescent dye-containing layer further contains a piperidine typehindered amine light stabilizer of tertiary amine structure which has amolecular weight of at least
 600. 6. Fluorescent retroreflectivesheeting of claim 5 wherein fluorescent dye-containing layer contains apiperidine type hindered amine light stabilizer in an amount 0 to 1 PHR.7. Fluorescent retroreflective sheeting of claim 1 whereinretroreflective layer and/or surface-protective layer and/or fluorescentdye-containing layer include an ultraviolet absorber.
 8. Fluorescentretroreflective sheeting of claim 7 wherein ultraviolet absorber is oneof benzotriazole type or of benzophenone type.
 9. Fluorescentretroreflective sheeting of claim 1 wherein retroreflective elementlayer comprises cube-corner type retroreflective elements. 10.Fluorescent retroreflective sheeting of claim 9 wherein cube-corner typeretroreflective elements are triangular-pyramidal cube-cornerretroreflective elements.
 11. Fluorescent retroreflective sheeting ofclaim 1 wherein retroreflective element layer comprises micro glassbeads type retroreflective elements.
 12. Fluorescent retroreflectivesheeting of claim 1 wherein resin which constitutes retroreflectiveelement layer are polycarbonate resins, (meth)acrylic resins, vinylchloride resins or urethane resins.